Raman scattering by coupled LO-phonon—plasmon modes and forbidden TO-phonon Raman scattering in heavily doped $p$-type GaAs

Raman scattering by coupled LO-phonon—plasmon modes of large wave vectors and forbidden TO-phonon Raman scattering have been measured in the first-order Stokes-Raman spectra of (100) surfaces of heavily doped $p$-type GaAs with concentrations ranging from ${10}^{17}$ to ${10}^{20}$ holes ${\mathrm{cm}}^{-3\mathrm{}}$. The wave-vector nonconservation and the breakdown of the selection rules are due to scattering by the ionized impurities. The measured peak positions, linewidth, and intensities of the LO-like and TO-like Raman lines are explained by postulating a wave-vector distribution of the modes created in the Raman process. Expressions for this wave-vector distribution which depend on the scattering mechanism involved are discussed.